1. Field of the Invention
This invention relates to the lubrication of metal sheet product, either bare or coated on one or both sides. Such sheet product, including foil gauge thicknesses thereof, is suitable for use in making formed food containers and trays, and for making industrial sheet products therefrom, including but not limited to fin stock, non-food lidding and numerous air handling equipment applications like spiral duct products. The invention further relates to aluminum sheet stock sold in an already lubricated state, ready for further processing. Industrial sheet product forms are also disclosed. Preferably this invention relates to making food- and/or beverage-contacting sheet product from such aluminum alloys as 1050, 1100, 1145, 3003, 3004, 5017, 5042, 5052, 5082, 5182, 5352, 8011 and 8111 aluminum (Aluminum Association designations), said products being made and sold in numerous tempers including but not limited to: 0, H19, and H24. An improved lubricant composition for such food and non-food sheet applications is also described.
2. Technology Review
The aluminum industry supplies food container and tray manufacturers with millions of pounds of flat or coiled sheet product each year. These manufacturers convert such sheet product into food-contacting containers in numerous shapes and sizes. Such sheet products are often coated with a lubricant composition on one or both surfaces by the sheet supplier, with additional lubricant being applied as required by the container and/or tray maker prior to fabrication. The beer and beverage industry also uses substantial quantities of lubricated aluminum product each year in their manufacture of container or can bodies and lidding. Any lubricant residue on food or beverage packaging must meet all applicable U.S. Food and Drug Administration (or "FDA") requirements. For numerous industrial, non-food contacting applications, FDA regulations are not an issue, however.
Liquid and solid lubricants are used in metal working operations to reduce and control friction and wear between the surface of metal being worked and surfaces of the apparatus carrying out a given metal working operation. Lubricants reduce and control friction and wear by maintaining a thin film of an appropriate composition between the contacting surfaces in relative motion. Lubricants can also improve tooling cleanliness and lifetime and provide good surface quality on the worked product.
In addition to their friction and wear reducing characteristics, lubricant compositions are expected to fulfill certain other requirements in sheet forming applications. They should: be easy to apply and remove where removal is warranted; afford some protection to the metal surface during handling and storage; present no health hazards to persons coming in contact with the composition; and cause no degradation of the surfaces in contact therewith. For food-contacting packages, lubricant residues should not affect characteristics, such as appearance, odor or taste, of the products packaged therein. They may help facilitate the initial packaging of foodstuffs in these containers, e.g., by aiding in the spreading of pie dough onto properly lubricated pie pans or "tins". In other instances, lubricants help facilitate separation of the food from the formed sheet containers or trays in which such foods are warmed, cooked or baked.
It is known to apply lubricant compositions to aluminum sheet products through numerous methods. One representative means employs an electrostatic spray coater or atomizer as set forth in commonly-assigned Grassel U.S. Pat. No. 4,839,202, the disclosure of which is fully incorporated by reference herein. Still other known lubricant application means include dipping the sheet product and/or passing it through any of various applicators which generate fine droplets of lubricant for deposit on said sheet product with electrostatic assistance, or between one or more rotating roll pairs designed to transfer lubricant to the sheet from the roll. The lubricant composition/blend of this invention can be applied by any of the foregoing means. On a less preferred basis, the lubricant composition of this invention may be added to one or more solvents prior to application of the solvent to the sheet metal, said solvent(s) being suitable for evaporation and recovery for reuse. Representative solvents include hexane and other common solvents, as well as many known water dispersed solvent compositions. For some sheet products, lubricated materials are further subjected to purposeful processing steps to impart mostly stylistic, but sometimes functional, improvements to surfaces which the consumer/end user most often sees or comes in contact with.